1. Field of the Invention
The present invention relates to a cleaning device for a fixing unit used in an electrophotographic apparatus such as a printer and a copying machine.
2. Description of the Related Art
In a conventional cleaning device for a fixing unit used in an electrophotographic apparatus, an actuator of a sensor is made to abut against an outer peripheral portion of an unused web whose diameter gradually decreases as the web is taken up, and the position of the actuator is detected by the sensor so as to detect a trailing end of the web.
In a conventional cleaning device for a fixing unit, a system is used in which the trailing end of the web is detected by detecting the outside diameter of the unused web by a sensor. However, the difference between the outside diameter of the unused web and the outside diameter of the shaft is small in the vicinity of the trailing end of the web, so that it has been difficult to discern whether or not the web still remains depending on the sensitivity of the sensor. In addition, since cleaning becomes faulty if the web is used up, it has been necessary to detect the trailing end of the web with sufficient leeway. For this reason, there has been a problem in that the unused web is wasted.
An object of the present invention is to solve the above problem.
To overcome the above-described problem, in a cleaning device for a fixing unit in accordance with the invention, a notched portion is formed in a winding shaft, which has an unused web wound therearound, at a position opposing a detecting position of a sensor. When a trailing end of the web comes to be exposed, and the web is disengaged from the wining shaft, the diameter of the notched portion of the winding shaft is measured although the diameter of the web was being measured up until then, so that the diameter changes substantially. For this reason, an output of the sensor also changes substantially, and the trailing end of the web can be detected easily without being affected by the sensitivity of the sensor.
In the cleaning device for a fixing unit having the above-described arrangement, the web may be impregnated with silicone oil to exhibit an oil applying function.